Stirrup Spacing Research Articles

Experimental investigation of GFRP‐reinforced concrete columns made with waste aggregates under concentric and eccentric loads

AbstractNowadays, reducing the waste and recycled material resources in nature and environmental protection, as well as reducing the use of natural resources, has gained the attention of engineers and researchers. One of the ways to reach this goal is to use waste and recycled materials in new concrete members' construction. Additionally, using glass fiber‐reinforced polymer (GFRP) rebars has gained high consideration owing to their advantages such as high tensile strength and corrosion resistance. Therefore, this study aims to measure the influence of recycled coarse aggregates (RCA) on the structural performance of reinforced concrete (RC) columns reinforced by GFRP rebars under concentric and eccentric loading conditions. A total of 24 RC columns were cast and subjected to concentric and eccentric loads with different eccentricity ratios (e/h):0 (no eccentricity), 0.25 (moderate eccentricity), and e/h = 0.5 (high eccentricity). A total of 18 columns were strengthened with longitudinal GFRP rebars, and six specimens were considered control samples reinforced by steel rebars. RCA was used at two contents of 0% and 100% in terms of weight as a substitute for natural coarse aggregates (NCA). In addition, to measure the influence of transverse reinforcement, three different spacings were considered: 60, 120, and 180 mm. Evaluation of axial behavior, the strain of rebars and concrete, and the ductility were the main aims of this study. Moreover, a comparison between the experimental results and existing standards was carried out. Findings revealed the adequate axial resistance of specimens when RCA was used. Therefore, RCA incorporation improved the axial resistance of GFRP‐RC columns by about 25% and 35% when the stirrup spacing declined by 60 and 120 mm, respectively in comparison with the same specimens made with NCA. However, the influence of RCA on the RC columns' axial behavior was declined by raising the eccentricity distance.

Study on the seismic performance of regional confined concrete columns

This paper experimentally investigated the seismic performance of three regional confined concrete columns (RCCCs) and three normal confined concrete columns (NCCCs) subjected to low cyclic loading under a high axial compression ratio. The crack development and failure mode were studied. The effects of the axial compression ratio and stirrup form on the behavior (i.e., hysteretic behavior, stiffness, ductility and energy dissipation) of confined concrete columns were studied. The experimental results suggest that both NCCCs and RCCCs have good bearing capacity and ductility, and their failure modes are similar. At the same axial pressure ratio, the ductility and energy dissipation capacity of RCCCs are 5% and 10% higher than those of NCCCs respectively. The best load carrying capacity and energy consumption of the confined concrete columns are achieved when the axial compression ratio is 1.1. Furthermore, a finite element analysis was conducted to simulate the behavior of the RCCC. The results of the finite element analysis agree with the test results. The simulated results show that the peak load and cracking load of the RCCC decrease with increasing stirrup spacing.

Hole layout calculation method of reinforced concrete beam demolition with soundless chemical demolition agents: Experimental investigation

Nowadays, urban renewal is accompanied by the demolition of a large number of obsolete buildings. The pollutions caused by blasting demolition have a serious adverse impact on the environment. Soundless chemical demolition agents (SCDAs) are put forward as a green and environment–friendly demolition method and have the potential to solve the pollution problems in the blasting demolition of concrete buildings. To this end, this paper aims to investigate the key problems in reinforced concrete beam demolition with SCDAs. The tests on 18 reinforced concrete beam specimens were carried out. The fracture phenomenon and failure mechanism were analysed. The expansive rate of SCDAs was proposed as the crushing effect index to investigate the impacts of hole diameter, hole spacing, concrete strength, stirrup spacing, and stirrup diameter. Besides, the influence mechanism of the stirrups was explored in depth, in which SCDAs in the hole were considered to be constrained by the surrounding concrete, and the stirrups were considered as the enhancement to the constraint of concrete. Eventually, a new hole layout calculation method was proposed, which accorded well with the experimental results.

Compressive behavior of concrete-filled ultra-high performance concrete tube with FRP stirrups

Ultra-high performance concrete (UHPC) has excellent durability, compressive strength and toughness which can be combined with normal strength concrete (NSC) columns to improve the performance. In order to investigate the compressive behavior of concrete-filled UHPC tube, twelve circular composite columns with carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) stirrups were tested. The effects of stirrup spacing and type on the axial behavior and failure mechanism of the composite columns were further analyzed. The research proved that the large-area spalling of the UHPC tube did not occur and the UHPC tube worked well with the internal concrete. Reducing the stirrup spacing and using the CFRP stirrups could significantly improve the ductility of specimens, but it had little influence on the initial stiffness. Then, a three-dimensional meso-scale model considering UHPC as two-phase material which composed of steel fibers and UHPC matrix was established. The simulated errors of the key mechanical performance indexes were almost within 15%, indicating that this finite element model could effectively reflect the compressive behavior of the concrete-filled UHPC tube columns. The influence rules of other variables including internal concrete strength, UHPC tube thickness and stirrup elastic modulus on the initial stiffness and peak load of specimens were also studied based on the validated model. Furthermore, the axial bearing capacity of the concrete-filled UHPC tube was predicted.

Enhanced Torsion Mechanism of Small-Scale Reinforced Concrete Beams with Spiral Transverse Reinforcement

The nonlinear torsional behaviour of small-scale reinforced concrete (RC) beams with continuous staggered spiral as transverse reinforcement stirrups is experimentally investigated. Twelve miniatures RC beams were tested under torsion load considering the closed shape of stirrups and compared with continuous staggered spiral ones. All miniatures beams were scaled down to be one-eighth the prototype beam size. The main parameters considered in this research are stirrup spacing and its configurations. Small scale RC beams were taken into account in the existing study because of their construction simplicity and financial feasibility. Mortar without coarse aggregate was applied instead of concrete to reduce the size effect of applying small scale models. Ongoing research trials have been carried out to obtain an efficacious approach to boost torsion failure mechanisms because brittle torsion failure of RC structural elements should be avoided. This study emphasized boosted torsion capacity, dissipated energy, and helical crack propagation. During testing, the primary cracking torsion moment, ultimate torsion moment, peak twist angle, and failure mechanism of the beams were inspected. The use of spiral stirrups showed great enhancement of the torsional behaviour of samples. It was observed that using spiral stirrups rather than closed stirrups could result in a substantial increase in torsion capacity and dissipated energy of 87.7% and 89.8%, respectively. As a result, the predicted capacities of the RC beams prototype were estimated in detail, taking account the scale down factor implemented by the authors. Values obtained based on international specifications and guidelines were used to compare the experimental results. Doi: 10.28991/CEJ-2022-08-11-019 Full Text: PDF

Effect of type, amount and configuration of reinforcement in HSC box-girders reinforced with BFRP bars and steel stirrups under torsion-shear-bending

There has been no research on the performance of high-strength concrete (HSC) hollow members reinforced with basalt fiber reinforced polymer (BFRP) bars and steel stirrups under combined torsion (T), shear (V), and moment (M); this study examines the above scenario. Six specimens of identical size and length were constructed and tested, each having a total quantity of reinforcement of 2.5%. The supports were restrained against twisting and the load was applied at a transverse eccentricity of 1.67 m at midspan, producing the required T-V-M ratio, with torsion as the dominant action. The proportion of longitudinal to transverse reinforcement, the number and diameter of longitudinal BFRP bars, and the diameter and spacing of steel stirrups, were the factors investigated. The experimental results were evaluated in terms of strength and stiffness, deflection and angle of twist, cracking pattern, and failure modes. For the same total amount of reinforcement, the best results were achieved utilizing specimens with BFRP bars and steel stirrups of smaller diameter at closer spacings. Employing more longitudinal BFRP bars ( ρ l = 1.58 ρ t ) produced better outcomes than using more steel stirrups ( ρ t = 1.32 ρ l ), indicating that the amount of BFRP bars is as critical as or more important than the amount of steel stirrups. The experimental results of cracking torque and twist, and ultimate torque were compared to the code and other available expressions. It was found that ACI, CSA, and EC equations can be extrapolated without any modification to predict the torsional strength of HSC box-girders longitudinally reinforced with BFRP bars under combined T-V-M. In addition, a new approach was suggested, which can predict the ultimate torsional twist capacity reasonably well.

Axial compressive behaviors of engineered cementitious composites-encased concrete filled steel tube columns after fire exposure

Engineered cementitious composite (ECC)-encased concrete filled steel tube (CFST) column, which is composed of outer steel reinforced ECC and inner CFST components, has broad application prospects in high-rise buildings due to its higher strength and ductility than the concrete-encased CFST column counterpart. This paper investigates the fire performance of ECC-encased CFST columns under and after fire exposures. Totally thirteen ECC-encased CFST columns and two concrete-encased CFST columns were prepared and tested considering different parameters, i.e., heating-up time, stirrup spacing and fire sides. It was found that the outer ECC component provides better fire protection to the inner CFST than the conventional concrete. Besides, the axial compressive strength and ductility of the ECC-encased CFST column were 32.2 % and 10.3 % higher than those of concrete-encased CFST columns after fire exposure. A finite element (FE) model and design equations were also proposed and verified by the experimental results, which could be applied to simulate and predict the compressive behavior of ECC-encased CFST columns after fire exposure.

Investigation on Improvement in Shear Performance of Reinforced-Concrete Beams Produced with Recycled Steel Wires from Waste Tires

In parallel with the increase in vehicle sales worldwide, waste tires are becoming an increasing problem. The storage and disposal of these waste tires are critical environmental problems. Re-using these wastes in different areas instead of being disposed of is vital in preventing environmental pollution and creating new low-cost products. From this motivation, this paper investigates the properties of traditional reinforced-concrete beam with recycled steel wires (RSWT) obtained from the waste tires. RSWT were added to reinforced-concrete beam between 1% and 3% by weight with an increment of 1%. In total, 9 cubes, 12 cylinders and 12 reinforced-concrete beams were cast and tested to obtain the compressive, splitting tensile and flexural strengths, respectively. RSWT added to the concrete by 1%, 2% and 3% increased the compressive strength by 17.2%, 30.8% and 46.4%, respectively, compared to the reference concrete. In split tensile strength, 14.4%, 25.1% and 36.7% increases were observed, respectively. This showed that there was an effective increase in the compressive and tensile strength of concrete with the increase of fiber content. Although the effect of fiber content in samples with high stirrup spacing (27 cm) provides significant benefit in improving the beam behavior, the effect of fibers was more limited as the stirrup spacing decreased (20 cm and 16 cm). An approximation of over 91% was obtained between the analytical calculations and the experimental results. This shows that the analytical calculations given in the standards can be used for new experimental studies.

Corroded reinforced concrete columns strengthened with basalt fibre reinforced ECC under axial compression

This study presents an experimental investigation aimed at evaluating the effectiveness of basalt fibre reinforced engineered cementitious composite (FRECC) in strengthening corroded reinforced concrete (RC) columns. In this strengthening technology, ECC acts as both a matrix for bonding basalt fibre and a new cover replacing the damaged concrete cover. A total of 34 specimens were tested under axial compression. The studied parameters were the number of basalt fibre layers, corrosion ratio of steel reinforcements and stirrup spacing. The experimental behaviour was characterized in terms of axial load-axial shortening curves and tensile strain development in stirrup and basalt fibre. The test results showed that FRECC composites significantly improved the performance of corrosion-damaged columns, and the strengthened columns gained peak load and ductility enhancements of 5%–62% and 160.0%–415.2%, respectively. The monitored strains revealed a possible interaction between basalt fibres and steel reinforcements and the influence of steel corrosion, and the fibre efficiency ratios at peak load and at 85% peak load in the decreasing branch were 0.10–0.48 and 0.25–0.62, respectively.

Torsional capacity evaluation of RC beams using an improved bird swarm algorithm optimised 2D convolutional neural network

This study presents the application of deep learning technology in torsional capacity evaluation of reinforced concrete (RC) beams. A data-driven model based on 2D convolutional neural network (CNN) is established, where model inputs contain the beam width, beam height, stirrup width, stirrup height, concrete compressive strength, steel ratio of longitudinal reinforcement, yield strength of longitudinal reinforcement, steel ratio of transverse reinforcement, yield strength of transverse reinforcement and stirrup spacing. To enhance the prediction accuracy of the proposed model, an improved bird swarm algorithm (IBSA) is leveraged to optimise the hyperparameters of CNN in the training phase. A comprehensive dataset, comprising 268 groups of laboratory tests of RC beams collected from published articles, is used for model development and validation. The results show that the proposed 2D CNN with hyperparameter optimisation exhibits high performance in predicting torsional strength of RC beams, which outperforms other machine learning models, building codes and empirical formula in terms of a series of evaluation metrics.

Analysis of concrete beams reinforced by GFRP bars with varying parameters

Abstract Structural buildings consist of concrete and steel, and these buildings have confronted many challenges from various aggressive environments against the materials manufactured from them. It contains high water levels and buildings whose concrete cover may be damaged and thus lead to the deterioration and corrosion of steel. It was important to have an alternative to steel, such as the glass fiber reinforced polymer (GFRP), which is distinguished by its great effectiveness in resisting corrosion, as well as its strong tensile resistance. Still, one of its drawbacks is that it has a low modulus of elasticity. This research article aims to conduct a numerical study using the nonlinear finite element ABAQUS program on eight beam models with various parameters such as stirrup spacing, compressive strength, reinforcement layer, and type of bar reinforcement under four-point bending. The result shows that the ultimate load capacity of the GFRP beam is higher than that of a beam reinforced with steel and the number and width of cracks are greater in the GFRP-reinforced beam than in the steel-reinforced beam. In general, the serviceability reflected by cracks and deflection is lower in GFRP-reinforced beams than in steel-reinforced beams with higher serviceability. The results, on either hand, showed the expected behavior of GFRP, which is linear elastic to the failure stage. These beams are divided into four groups of beams with different variables studied to understand GFRP bars’ behavior under static loading. The variables taken in this study are the spacing between the stirrups, the compressive strength of concrete, the effect of the number of layers of reinforcement, and the type of reinforcement bar.

Experimental Study of Hollow RC Beams Strengthened by Steel Fiber under Pure Torsion

This paper examines the effectiveness of pure torsional loads on hollow reinforced concrete high-strengthened beams. Engineers need to know how much twist a structural member generates when exposed to torsional loads to design it properly. This is done through an experimental investigation of the torsional behavior of reinforced concrete (RC) beams using twelve hollow rectangular beams with varying parameters, such as the spacing of the stirrups, the influence of the steel fiber fraction, and the main reinforcement amount. Four values of fiber volume fractions (0, 0.5%, 0.75%, and 1%), three spacings of transverse reinforcements (60,100, and 150 mm), and various longitudinal reinforcements (8Ф12 mm, 6Ф12 mm, and 4Ф12 mm) have been used. The tested beams had the same length (1000 mm), cross-sections, concrete mixture, and quality control. In the hollow beams, the interior dimensions were 180 mm × 180 mm, while the exterior dimensions were 300 mm × 300 mm. Torsional loads were applied to all the beams using custom-built test equipment. This study highlighted that the structural characteristics of hollow RC beams could be improved by increasing the fiber volume, lowering the stirrup spacing, and increasing the longitudinal reinforcement. Torsion moments rose by 132% when the fractional volume of fiber was increased from 0% to 1%, while they rose by 71.27% when the longitudinal reinforcement was increased from 4 to 8 bars for beams with fractional volumes of fiber of 0.5 percent and the same transverse reinforcement ratios.

Analysis of influencing factors on axial compression performance of BFRP bars-coral reef and sand concrete columns

A more systematic analysis of the factors influencing the axial compression performance of basalt-fiber-reinforced polymer (BFRP) bars-coral reef and sand concrete (CRSC) columns was carried out based on axial compression load capacity tests on 15 columns in 5 groups. The test study factors include the concrete strength, longitudinal bars diameter, stirrup spacing, slenderness ratio and bars type, and type of bars material. The results show that the damage process of BFRP bars-CRSC columns can be divided into elastic stage, cracked stage and damage stage. Under different diameters of longitudinal bars, increasing the diameter of longitudinal bars leads to the reduction of the adhesion between longitudinal bars and concrete protective layer, which reduces the load-bearing capacity; decreasing the spacing of hoop bars helps to improve the ductility of the member, but it also reduces the continuity of CRSC and the strength.

Mechanical Property Analysis and Calculation Method Modification of Steel-Reinforced High-Strength Concrete Columns.

The existing studies lack research on the ductility of steel-reinforced high-strength concrete (SRHC) columns and current specifications restricted the use of high-strength concrete in steel-reinforced concrete (SRC) columns. To compensate for the shortcomings of the existing research and promote the application of high-strength concrete in SRC structures, we test six SRHC columns and one SRC column to examine the effects of the steel content, eccentric distance, and slenderness ratio on the ductility, bearing capacity, and failure mode of SRHC columns. Further, Abaqus finite element models are established to predict the influences of more parameters on post-peak ductility and analyze the relationship between strain development of the concrete and the decrease in bearing capacity of SRHC columns. The results show that the penetration of cracks into aggregate during failure is the primary reason for the poor ductility of the SRHC columns. Improving the confinement effect of the stirrups on concrete is the most effective measure to enhance the ductility of the SRHC columns. The decline in the stirrup spacing from 100 mm to 50 mm increased the ductility coefficient from 1.47 to 5.56. The effect of the steel content, stirrup strength, and slenderness ratio on the ductility coefficient of SRHC columns is less than 30%. After analyzing the reason for the error of current specifications, a modified formula with an error of less than 5% is developed.

Axial compression behavior of core-steel tube with T-shaped flanges reinforced concrete column

A novel core-steel tube with T-shaped flanges reinforced concrete (CSTRC) column is proposed. The steel skeleton of CSTRC columns consists of a core-steel tube with T-shaped steel welded around the steel tube. Ten CSTRC column specimens and one contrast specimen without core-steel tube are tested to examine their axial compression behavior. The effects of the cross-section form of core-steel tubes, the steel flange width, steel flange thickness, steel web height, and volume ratio of stirrups on the failure mode and bearing capacity of CSTRC column are also methodically investigated. Furthermore, finite element models are developed to conduct parametric studies to determine how the strength of both the concrete and the steel skeleton affects the bearing capacity and ductility. Finally, a calculation formula to predict the axial compression bearing capacity of CSTRC columns is established. The test results reveal that: (1) compared with the contrast column, all CSTRC columns exhibit good bearing capacity, with a better deformation regime; (2) the cross-section form of core-steel tubes has little influence on the bearing capacity of CSTRC columns, but demonstrates great impact on its ductility. Additionally, growing the width and thickness of the steel shape flange and lessening the stirrup spacing enhances the ductility of CSTRC columns; (3) increasing the strength of both the concrete and the steel skeleton improves the bearing capacity of columns, but decreases the ductility; (4) the prediction results calculated by the proposed approach agree well with the experimental results, which confirms the suitable accuracy of the proposed method.

Experimental study on seismic behavior of T‐shaped steel fiber reinforced concrete columns

AbstractSix T‐shaped columns in which steel fiber concrete is integrated with a high‐strength stirrup (SFRC) and two control specimens are tested under a cyclic lateral load and constant axial load. The effectiveness of the steel fiber concrete and high‐strength stirrup to enhance its ductility and earthquake resistance is described at high‐and low‐axial compression ratios. The failure patterns, hysteresis response, backbone curves, ductility, and strain behavior analysis of the columns are studied systematically in the test. The effects of the stirrup strength, stirrup spacing, steel fiber content, and axial load ratio were investigated. The test results demonstrated that all specimens exhibited flexural failure. Steel fibers could prevent the cracked concrete from spalling. Specimens with high‐strength stirrups, close stirrup spacing, and steel fiber exhibited a higher lateral bearing capacity, energy dissipation capacity, initial stiffness, and displacement ductility. A new strength model for predicting the lateral ultimate capacity of T‐shaped concrete columns strengthened with SFRC subjected to cyclic loading is proposed. The calculated results agree well with the test results. Eight T‐shaped column specimens were simulated using ABAQUS finite element analysis software. A comparison of the results of the numerical study with the experimental results demonstrates that the finite element model can accurately predict the structural behavior.

The effect of stirrup spacing and hook angle on RC cantilever beams with iron chip waste

In this study, the usability of industrial iron chip waste was investigated to carry out recycling in the production of reinforced concrete (RC) cantilever beams with different stirrup spacings and hook angles. In the concrete produced for cantilever beams, aggregates no larger than 4 mm diameter were reduced by 20% and replaced with iron chip waste. Cantilever beams were manufactured with stirrup spaces of 50, 100 and 150 mm. The hook angles of the stirrups were differentiated to be 90 and 135°. The experimental set-up was prepared in such a way that one side of the samples was fixed and the other side was free. Load–displacement curves of cantilever beams were obtained. In the research, it was observed that although cantilever beams with 20% iron chips experienced a decrease in their strength compared with the reference beams, they increased their ductility values at all three different stirrup spaces. As the stirrup spacing widened, the ductility values decreased. However, the effect of iron chip additives on ductility increased. Samples with a stirrup hook angle of 135° increased in both strength and ductility values compared with samples with a stirrup hook angle of 90°.

Experimental study on spatial mechanical properties of grout anchor lap joints

To study the anchoring performance of non-concentric and multi-medium lap joints of grout anchors, pull-out experiments of 18 groups of specimens were implemented. The main focus of this study is the influence of steel bar diameter and anchorage length on the bond and anchorage performance when the diameter of metal bellows and spacing of spiral stirrups are fixed. Qualitative and quantitative analyses are conducted to experimentally ascertain the mechanical safety of structures. The finite element method is employed to replicate crack development and mechanically simulate the segment model. The simulation results are analyzed and compared with experimental data. When the anchorage length is 35d–40d (where d is the diameter of the embedded steel bar), no component is damaged, indicating that the anchorage length is stable and reliable. However, when the anchorage length is less than 15d, slip failure occurs. In this work, a comprehensive description of the mutual restriction and force transmission variation law of each component of the node under the action of stress based on the strain distribution analysis of the multi-media coupling model is provided. Moreover, optimization suggestions for the structure are proposed. The results of this study provide experimental support for the application of this type of joint in prefabricated building structures.

Numerical Simulation of Lap-Spliced Ultra-High-Performance Concrete Beam Based on Bond–Slip

In this paper, 3D finite element simulations were conducted for lap-spliced ultra-high-performance concrete (UHPC) beams using ABAQUS software. Based on the concrete damaged plasticity (CDP) model, the plastic damage factor was introduced to simulate the material properties of UHPC. The nonlinear characteristics of the steel bar and UHPC were considered, and the bond–slip constitutive relationship was selected to evaluate the bond–slip between the lap-spliced steel bar and UHPC. The simulated load–deflection curve, peak load, bond strength, and failure mode were in good agreement with the experimental results. The verified finite element model was used to analyze the parameters of the lap-spliced UHPC beam. The effects of lap-spliced steel bar diameter, stirrup spacing of non-lap segment, and shear span ratio on the mechanical properties and bond properties of the lap-spliced UHPC beam were studied. This study can provide a reference for the future simulation and design of lap-spliced UHPC beams.

Analysis of bond performance of steel bar in steel-polypropylene hybrid fiber reinforced concrete with partially recycled coarse aggregates

To promote structural sustainability and resource recycling, the bond performance between steel bars and steel-polypropylene hybrid fiber reinforced recycled aggregate concrete (HFRAC) confined with/without stirrups was investigated through the pullout test on 72 specimens. The specimens with varying stirrup spacing, polypropylene fiber volume fraction, and steel fiber volume fraction were designed, and the replacement rate of recycled coarse aggregates was kept at 50% for all specimens. The strain gauges were bonded in the slotted steel bar of specimens for detecting the strain of steel bar during the loading process. According to the measured strain of steel bar, the distribution law of bond stress and relative slip for the specimens with/without stirrups were analyzed. Results showed that the lateral confinement of stirrups dramatically improved the bond stiffness and rendered the distribution of bond stress more uniform than that of specimens without stirrups. The hybridization of steel fiber and polypropylene fiber improved the bond strength of recycled aggregate concrete specimen without/with stirrups, in which the stirrup spacing were taken as 80 mm and 40 mm up to 12%, 8.97% and 5.69%, respectively. Smaller stirrup spacing leaded to a slight reduction in bond strength when 1.5% steel fibers were added into the specimens. Based on the thick-walled cylinder model and fictitious crack model reflecting the softening behavior of HFRAC under tension, the solutions of bond strength of steel bars in HFRAC with/without stirrups were deduced, respectively. Finally, the bond-slip model of steel bars in unconfined/well-confined HFRAC was proposed, which considered the effect of anchorage position.